War of the Mantuan Succession

The War of the Mantuan Succession, from 1628 to 1631, was caused by the death in December 1627 of Vincenzo II, last male heir from the House of Gonzaga, long-time rulers of Mantua and Montferrat. Their strategic importance led to a proxy war between the French-backed Duke of Nevers, and the Duke of Guastalla, supported by Spain. It is considered a related conflict of the 1618 to 1648 Thirty Years' War.

Fighting centred on the fortress of Casale Monferrato, which the Spanish besieged twice, from March 1628 to April 1629 and from September 1629 to October 1630. French intervention on behalf of Nevers in April 1629 led Emperor Ferdinand II to support Spain by transferring Imperial troops from Northern Germany, who captured Mantua in July 1630. However, French reinforcements enabled Nevers to retain Casale, while Ferdinand withdrew his troops in response to Swedish intervention in the Thirty Years' War, and both sides agreed a truce in October 1630.

The June 1631 Treaty of Cherasco confirmed Nevers as Duke of Mantua and Montferrat in return for minor territorial losses. More importantly, the treaty left France in possession of Pinerolo and Casale, key fortresses that controlled access to passes through the Alps and protected its southern borders. The diversion of Imperial and Spanish resources from Germany allowed the Swedes to establish themselves within the Holy Roman Empire and was one reason that the Thirty Years' War continued until 1648.